The game of golf has evolved over the years into a highly complex sport, with many technical innovations for the equipment involved. As played by the professional, any advantage is highly sought after, as any such advantage, even if providing perhaps only an average of a fraction of a stroke advantage over several games, can result in a one or two stroke advantage over a 72 hole match. Amateurs and weekend golfers have the same interest in improving their games, and also seek the most technologically advanced equipment which still falls within the rules, in order to gain the maximum possible advantage.
Accordingly, many technical improvements have been developed for the "irons" or metal headed clubs with which most play accomplished. These irons have evolved into a series of clubs, numbered from one to nine with a "pitching wedge" and/or "sand wedge" beyond the nine iron. These clubs each have a differently angled club head face, with the one iron being closest to the vertical (i. e., the club face being most nearly parallel to the club shaft), and the sand wedge having a club head face angled considerably away from the vertical. The remaining clubs fall into a range between the one iron and the sand wedge. The differently angled club faces will impart a different trajectory and spin to the ball when struck, with the one iron providing the lowest trajectory (least arc) and the least backspin, thus generally causing the ball to travel farther than the other clubs. A sand wedge will send the ball on a relatively short flight, with a highly arched trajectory, and will also impart considerable backspin on the ball, thus shortening its rollout or even causing the ball to back up after striking the ground.
As can be seen, generally the lower numbered irons are used for relatively long shots, while the higher numbered irons and sand wedge are used for shorter shots, where greater accuracy is required. Accordingly, the lengths of the club shafts are also varied, with the lower numbered irons having longer shafts, thus allowing greater speed for the club head during the swing to impart greater force to the ball, and the higher numbered irons and sand wedge having shorter shafts to provide a golfer with better control. Other variations (club head weights and the location thereof in the heads, external shaping and pattern of the club head face, etc.) have also been developed for the different clubs.
From the foregoing, it will be noted that the angle of the attachment of the club shaft to the club head at the hosel or shank of the club head (known as the "lie angle"), must vary according to the length of the club shaft in order to align the major axis of the club head parallel with the playing surface. Accordingly, the hosels and shafts of the lower numbered irons (with longer shafts) are generally angled further away from the perpendicular, and the higher numbered irons and the wedges are generally angled more closely toward the perpendicular due to the shorter shafts of such clubs.
At this point, it should be pointed out that in any dynamic situation (including swinging a golf club), there are two mutually exclusive concerns: Stability and control The more stable a dynamic device, the more difficult it will be to alter that stability to control the device. On the other hand, the less stable, the easier to control and cause the device to deviate from its stable mode. This is of interest relative to the set of iron golf clubs discussed herein, as it is particularly important to provide for ease of control with the higher numbered clubs, in order to provide for more accurate placement of the relatively shorter shots made with such clubs, generally closely approaching the green and the hole. Conversely, control is not so important with the lower numbered clubs, where stability is of paramount concern for greater consistency on each shot.
These tradeoffs between stability and control of the various iron clubs in a set have heretofore generally been made by shifting the center of gravity of each of the club heads, which affects the moment of inertia of the club. However, another means of altering the moment of inertia is by shifting the distance of the hoseI from the center of gravity of the club head, and this method may have definite advantages over shifting the centers of gravity of each of the club heads. While such hosel shifting has been accomplished before, it has heretofore always included a shift of the centers of gravity of the club heads in combination with the hosel shift.
Accordingly, the need arises for a means of providing greater stability for lower numbered irons of a golf club set, and greater control for higher numbered irons, by respectively shifting the hosel of the club away from the center of gravity of the club head for the lower numbered irons, and toward the center of gravity for the higher numbered irons. The club heads may retain a common center of gravity, if desired, with the hosel shift accomplishing all of the moment of inertia change required for the desired stability and control.